Costs related to the Sprinter train shutdown have increased sharply in recent weeks and could crest at $3 million, according to a review of purchase requests made by the North County Transit District.

The largest single request for spending — up to $1.8 million for additional replacement bus service from contractor First Transit — was approved Thursday during the agency’s board of directors meeting in Oceanside.

It adds to the maximum $664,780 contract the board approved in March for charter bus service provided by U.S. Coachways and the $656,571 purchase contract for Sprinter replacement parts either requested or already approved by the board.

The maximum value of those contracts totals $3.15 million.

Transit officials have closed the Sprinter light-rail network since March 9 because of the trains’ accelerated brake-rotor wear. Replacement buses and some contracted vans and taxis have ferried the thousands of riders who relied on the rail line, which runs between Oceanside and Escondido.

Deborah Castillo, a spokeswoman for the agency, said the officials are “aggressively” working to recoup expenses related to the shutdown from the train’s maintenance contractors.

She also said the district had “no comment” on how much it has spent during the Sprinter shutdown, on what it is doing to contain those costs and whether it expects significant additional expenses.

Officials said in late April that Sprinter trains could be back “within weeks,” noting that early test runs on trains with newly installed brake parts have been successful.

At Thursday’s meeting, no date for resumption of service was provided.

Agency officials have said they are investigating what caused the advanced wear on the brake rotors, but have yet to release any findings.

Richard Berk, the transit district’s former head of rail maintenance, said in March that the state’s stringent brake performance standards were to blame for the rotors wearing out faster than expected. Berk resigned March 1 after state inspectors found the advance wear. Berk said that over several years, he had repeatedly informed his supervisors at the transit district about the pending problem.

District officials have said there are no written records to back up Berk’s statements.